Deep venous thrombosis (DVT) is the most common cause of venous outflow obstruction. Venous outflow obstruction may be either acute or chronic. Patients with acute DVT usually present with sudden onset of unilateral leg swelling. This is often painful, associated with cyanosis of the extremity, and often after prolonged immobilization or sedentary activity. Chronic venous outflow obstruction usually occurs months to years after an initial DVT. In symptomatic patients, the body's own recanalization of thrombosed veins is incomplete, and the collateral circulation is inadequate. The proximal obstruction results in distal venous hypertension, lower extremity swelling, and pain worsened after ambulation. Although venous outflow obstruction of the lower extremity may involve the entire venous system, some endovascular techniques focus treatment on thrombosis of the largest veins, namely, the inferior vena cava (IVC), common iliac vein, and external iliac veins.
Catheter-directed thrombolysis and percutaneous mechanical thrombectomy (PMT) can be important therapies in patients with acute DVT, largely replacing venous bypass surgery. Initial clinical and technical success can be achieved in most patients with acute DVT. Early thrombus removal results in relief of lower extremity venous hypertension and improved long-term patency of the venous system.